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Tuesday, July 13, 2010

Rotors Part 2

It turns out that drill bits track slightly when drilling. This means that drilling all the way through (34mm) my rims for the alignment pins and 4-40 screws is a bad idea. This also means that I had to drill halfway and flip the part over (doubling the number of holes I had to drill to 80...). I also knew there'd be no way to get a perfect alignment, so I just offset the two sets of holes.

The mill work went smoothly. Just put them in the EZ-Trak, found center with a gauge thingy, programmed a drill circle, did a pass with a center drill, a pass with an 1/8" skipping every other, and the other holes with a #43. Then stop, flip, and repeat. The angle holder thing brought deflection down to only a few thousandths.

I probably made over 1000 pecks over the course of all 4 repetitive and soooo dull. But the results were pretty dang good.

Next came tapping the 40 4-40 holes.

So, 40 holes with a small tap...guess what happens.

Oh well, that's ok. At least I only snapped one. I just moved the hole over a little.

Drilling into the magnetic flux ring seems like a bad idea in terms of magnetics and saturation...and it is, but luckily the holes will be (mostly) filled with steel pins/screws. After spending 16ish hours on these things, I'm starting to like the can threading method better.

Next Step

The next step is to get that rotor to fit in that tire. This requires boring out the inside of the wheel. The only way without making some time consuming compression jig was to put the tire in a giant chuck, use a boring bar to try and bore out the inside, and hope the thing doesn't deform. Oh, and hope that the boring bar can cut the rubber.

So far so good

The hard plastic cut like a dream. But when I got to the rubber...

...small chunks of rubber started flying out. Then it started to deform, which is when I stopped. I did NOT want this thing flying at my face.

What a mess. Total fail. It turns out that instead of a hard plastic ring directly underneath the rubber tire, there are large plastic teeth, such that, when they molded the tire onto the plastic, rubber would go between the teeth. So when I cut the bases of the teeth off by boring out the inside, the teeth turned into plates that would hinge on the rubber between...resulting in a very flexible and totally worthless part for turning. But couldn't I just make a jig for it? I could, that would stop the deformation...but it turns out that turning rubber this soft is impossible without constantly freezing it with liquid nitrogen. Now that would be cool, but I'm not about to set it up.
In summary: This won't work. Crap.

So now what? I basically have two options:
1. Learn polyurethane molding. I've always wanted to learn how to do it, but I'm not sure I have the time right now. My basic plan would be to make a silicon mold from these tires or some large cylinder, then cast them in urethane. 

2. Find some urethane strip and glue it on the rotors, kinda like this (scroll down). 

We'll see how it goes. There's always a bright side, though:

Hell yeah.

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